Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in the field.
As is known in the art, positioning technologies generally operate by measuring the time a signal takes to traverse from a signal source to the receiving device. In most prior art applications, this measurement is taken by comparing the time at which a signal is sent with the time at which the same signal is received. Common positioning systems such as GPS use three or more such signals and, using trilateration, calculate an object's position. Since the measurement calculations are time-sensitive, a fourth signal is commonly required to ensure that the clocks of the source and the receiver are properly synchronised.
Multipath refers to the phenomenon whereby positioning signals are reflected off other objects, such as walls and furniture. This is especially prevalent in an enclosed environment, such as indoors, but is also a significant problem in built up areas, such as in cities. Simplistically speaking, reflected signals take longer to traverse from a source to a receiver, therefore affecting the accuracy of the measurements. Also the receiver sees conflicting signals originating from the same source, having different timing information. Some modern receivers use selection algorithms to try to determine the most appropriate signal to use in position determination. However, receivers typically cannot differentiate multipath signals from the genuine positioning signals to any high degree of accuracy.
Also known in the art are phased arrays, consisting of a number of antenna elements that can be individually controlled to direct a beam. In a typical phased array, signals received at each element are individually phase and gain manipulated, the exact manipulation required depending on the direction of the beam required. The resulting phase and gain manipulated signals from each element are then summed to obtain the desired direction of the beam.
There are three main forms of phased array antennas in use today:                a) fixed beam forming;        b) sequential beam forming; and        c) simultaneous beam forming.        
Fixed beam forming antenna arrays have a fixed phase relationship between the elements and can only direct their beam in a single direction. Since the direction of the beam is fixed, this type of antenna cannot be used individually to track a moving signal source in a positioning system, such a satellite in a GPS application. A fixed beam forming antenna must be used in conjunction with some mechanical means to steer the beam to the transmission source. Aside from reliability issues related to long term use of mechanical equipment, this mechanical movement must be coordinated with the direction in which the beam is pointed. This adds an additional source of potential error.
Sequential beam forming phased array antennas use discrete phase and gain circuitry attached to each element to form beams sequentially in multiple directions. Discrete circuitry is required because each element must be individually controlled. Therefore, each element must have access to its own suite of electronics, such as phase shifters, variable gain amplifiers, and associated control signals. Apart from the additional costs arising for all the required discrete circuitry, and the problems introduced in controlling this circuitry with the precision required, this method is severely constrained when used in positioning systems because only a single beam can be directed at a time. As noted above, positioning systems such as GPS require the tracking of at least three signals, and to get the most accurate results these signals should be tracked simultaneously. Sequential beam forming phased arrays are therefore not suitable for use in positioning systems because they cannot track more than one signal simultaneously.
Simultaneous beam forming phased array antennas are also widely in use. Traditional simultaneous beam forming antennas use large arrays of elements with complex circuitry to simultaneously form beams in multiple directions. These arrays require RF front ends and analogue-to-digital converters for each element, and a very complex array of digital logic in the baseband to combine all the element signals together. The size, power consumption, and cost of such arrays limit their use to very large installations typically using hundreds of elements, for example in military applications. Clearly, the size, complexity, power consumption and cost of these systems make them unsuitable for use in positioning systems.
Additionally for positioning systems using interferomic techniques, any line biases or group delays introduced by the large scale parallel processing of traditional simultaneous beam forming antenna arrays cannot be tolerated. All these errors must be estimated and calibrated out of the system for centimeter positioning accuracies to be achieved. This is a non-trivial problem as these biases will change with circuit temperature, voltage, and component tolerances. Again, this makes traditional simultaneous beam forming antenna arrays unsuitable for use in high precision positioning systems.